As an image forming apparatus which undergoes an electrophotographic process involving electrostatic charging, exposure, development and transfer to form an image there has heretofore been known one comprising a cleaning blade made of an elastic material such as rubber for cleaning the surface of an electrophotographic photoreceptor from which a toner has been transferred. The use of a cleaning blade comprising an abrasive material incorporated in a rubber material has been proposed to remove attached materials from the surface of the electrophotographic photoreceptor efficiently (see Patent References 1 to 4 shown below).
Further, the use of a cleaning device comprising an auxiliary brush disposed in contact with the electrophotographic photoreceptor above the cleaning blade has been proposed (see Patent Reference 5 shown below). In the cleaning device, attached materials are peeled off the surface of the electrophotographic photoreceptor by the auxiliary brush. The attached matters having a lowered attraction force are then removed by the cleaning blade.
Patent Reference 1: JP-A-61-239279
Patent Reference 2: JP-A-317093
Patent Reference 3: JP-A-2001-296781
Patent Reference 4: JP-A-2002-162878
Patent Reference 5: JP-A-1-312578
In recent years, image forming apparatus have been developed to have higher operation speed and higher performance. At the same time, image forming apparatus have been required more and more to have a prolonged life. Accordingly, the various members constituting image forming apparatus have been required to have a higher reliability. However, the electrophotographic photoreceptor of the related art image forming apparatus leaves something to be desired in reliability.
In other words, in the case where a cleaning blade is used, the external additives for the toner, etc. are agglomerated on the edge of the blade. The vibration of the blade with the operation of the electrophotographic photoreceptor (stick slip phenomenon) causes the agglomerated material to be fixed to the surface of the electrophotographic photoreceptor, occasionally causing filming. This filming is a phenomenon which can be remarkably seen with color image forming apparatus which perform image formation by overlapping a plurality of color toner images.
It is very difficult to enhance the strength of both the electrophotographic photoreceptor and the cleaning blade in harmony with each other. When the strength of one of the two members is greater than that of the other, the member having a lower strength is often subject to damage. In some detail, the sliding movement of the electrophotographic photoreceptor and the cleaning blade with each other causes the electrophotographic photoreceptor or cleaning blade to be scratched, abraded or chipped. As a result, image defects can easily occur. In particular, in the case where a fine particulate toner having a spherical form having a reduced diameter is used for higher image quality, it is necessary that the contact pressure across the electrophotographic photoreceptor and the cleaning blade be predetermined high to prevent the toner from passing through the gap between the two members. This causes the electrophotographic photoreceptor or cleaning blade to be easily damaged. Further, when the contact pressure across the electrophotographic photoreceptor and the cleaning blade is predetermined high, the resulting bending of the cleaning blade or uneven rotation of the electrophotographic photoreceptor can cause the deterioration of image quality.
Moreover, in the case where the cleaning blade is used in combination with an auxiliary brush as in the image forming apparatus described in Patent Reference 5, the auxiliary brush can cause the surface of the electrophotographic photoreceptor to be scratched (scratch mark). Further, when the tip of the auxiliary brush repeatedly runs along the scratch mark as if it acts as a stylus, the surface of the electrophotographic photoreceptor is scratched more deeply than in the case where only the cleaning blade is used, resulting in remarkable deterioration of image quality.